A method and apparatus for forming a skid-resistant surface on a thermoformed object and more particularly a method and apparatus having a device for abrading the surface of a blank before thermoforming.
It is frequently desirable to form a non-slip or skid-resistant surface on the surface of thermoformed objects such as truck bed liners. Typically, truck bed liners are thermoforned from blanks of extruded plastic material. The plastic is extruded into a continuous sheet which is wider than necessary for the mold of a thermoforming machine. Typically a pattern is formed on one side of the sheet by embossing the top surface of the sheet with a roller having a pattern as the sheet exits the extruder. The pattern is typically formed to have a texture and appearance of leather. Although the roller forms indentations in the surface of the sheet, the surface is sufficiently smooth that cargo and the like can slide on the surface of the truck bed liner when a vehicle turns, stops or accelerates.
Accordingly, various methods have been employed by the manufacturers of liners to prevent movement of cargo. It is known as disclosed in U.S. Pat. No. 5,265,993 to Wayne to mount cross members or dividers above the floor of the liner to form a grid to hold cargo from movement.
It is also known as disclosed in U.S. Pat. No. 5,549,428 to Yeatts to form devices which have ribs which lock in the longitudinal grooves of the floor. The top surface of the device is formed of material which produces greater friction than the surface of the liner and thereby reduces movement of the cargo.
Finally, it is known to cover the top surface of the liner with a skid-resistant coating, such as disclosed in U.S. Pat. No. 4,693,507. However, the coating prevents the recycling of scrap liner material, thereby adding greatly to the cost of the liner.
Accordingly it is an object of the invention to produce a slip or skid-resistant surface for a liner which is economically produced.
A method and apparatus for producing a skid-resistant surface on items produced by thermoforming includes extruding a thermoformed sheet of material, abrading a top surface of the sheet to form a plurality of indentations, forming a blank of said thermoplastic material from said sheet, and thermoforming said blank to form a molded object and to open said indentations to form a skid resistant surface on said object. The abrading step may be accomplished by passing the sheet under a wire brush rotating in the same direction as the direction of travel of the sheet and at a slightly greater speed.
The apparatus includes a conventional thermoplastic extruding machine and a delivery mechanism to deliver the sheet from the extruder to an abrading station. The abrading station includes rollers for delivering the sheet to pass beneath a rotatable wire brush. The wire brush is mounted to extend transversely to the direction of travel of the sheet and is rotated in the same direction at a slightly greater speed by a motor. The apparatus also includes a conventional cutter to trim the sheet into rectangular blanks and a conventional thermoforming machine. A hood extends over the roller to collect material ground from the surface by the brush. Additionally, a receptacle may be mounted beneath the brush to collect the ground off material.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings which illustrate a preferred embodiment and wherein: